The present invention relates to a method for transmitting of data from a sender to two or more recipients, to a transmitting and/or receiving unit, and to a communications system.
In the case of many services and applications which are offered in modern mobile radio systems, the aim is to transmit messages not just to one mobile radio subscriber but to two or more mobile radio subscribers. Examples of services and applications such as these include news groups, video conferences, video-on-demand, distributing applications, etc.
Where messages are being transmitted to the various subscribers, it is possible to send each recipient a copy of the data separately. Although this technique can be implemented easily, it is not suitable for large groups, however. Since the same message is transmitted to a total of N recipients via individual connections or unicast connections, and is transmitted a number of times in the process over common connecting paths, this method requires a very wide bandwidth.
A better option is offered by multicast transmission. In this case, the various subscribers to which the same message is intended to be transmitted are combined to form a multicast group, which is allocated a multicast address. The data to be transmitted is then sent only once to this multicast address. The MC message is in the ideal case sent only once from the sender to the recipients via common connecting paths. The sender does not need to know where and how many recipients are concealed behind the multicast address.
In the case of broadcast, messages are sent to all the subscribers within a geographical region. A region such as this may, for example, be defined by a part of the overall network. As in the case of multicast, the broadcast message is ideally sent only once via common connecting paths from the sender to the recipients. Each subscriber has to carry out enabling settings on their respective terminal if he/she subsequently wishes to evaluate broadcast packets from a corresponding broadcast group. The subscriber can then determine whether he/she wishes to receive or reject all of the broadcast messages, or to receive only specific messages.
In the course of a known method for data transmission, a specific number of frames are typically always interchanged between a network and a mobile radio within a specific time. A frame is in this case a time structure on which, for example, in the case of UMTS, all of the signal processing and data transmission is based, see also [1].
If all of the frames are transmitted and received by the mobile radio continuously, this is referred to as continuous transmission or continuous reception. However, it is also possible, for transmission, to use interrupted reception or so-called discontinuous reception DRX in order, for example, to reduce the energy requirement of the mobile radios. When using DRX, the frames are not transmitted and received by the mobile radio continuously, but rather specific frames are omitted. In this mode, however, at least one specific subset of all of the frames or a subset of the possible frames must be transmitted in order to maintain the connection.
The present invention is, therefore, directed toward a method, a transmitting and/or receiving unit and a communications system for efficient, resource-saving and energy-saving transmission of data to a group of recipients on a point-to-multipoint service. In particular, is the present invention seeks to allow use for the purposes of a multimedia broadcast/multicast service MBMS.